The invention relates to a brake cylinder for pneumatically actuated vehicle brakes, in particular for commercial vehicles, and to a method for controlling the brake cylinder.
In heavy commercial vehicles, the parking brake is actuated by what are known as spring force accumulator cylinders (spring-loaded cylinders). Here, the brake actuating force is generated via spring force, with the result that the requirements for a mechanically actuated parking brake are satisfied.
Since the spring force accumulator cylinders are, as a rule, designed to generate very high forces, manual release in the operating case is no longer appropriate. In the case of pneumatically actuated brakes, the parking brake is therefore released by means of compressed air.
In order to make this possible, spring force accumulator cylinders are, as a rule, equipped with a release piston. It is possible by way of this piston, if compressed air is introduced, to compress the spring to such an extent that the brake is released. In order that the parking brake is not engaged while driving, the piston is loaded constantly with compressed air, with the result that the spring cannot be relieved and therefore the parking brake does not start to act.
The most common design is what is known as a combined cylinder. A combined cylinder includes or combines two different brake cylinder types, namely a spring force accumulator cylinder for the parking brake system (PBS) and a compressed air cylinder (usually a diaphragm cylinder) for the service brake system (SBS).
The two cylinders are usually arranged behind one another in an axial direction. The spring force accumulator part, which acts with its piston rod on the piston collar of the diaphragm cylinder and by the latter, in turn, on the brake lever, is arranged behind the diaphragm part of the combined cylinder.
This design requires a relatively large amount of installation space. However, the installation space is being limited increasingly by the introduction of more complex chassis systems, such as independent suspension systems, lightweight axles, etc.
There are therefore efforts to minimize the space requirement for the parking brake cylinder by other designs and methods of operation. To this extent, what is known as a compact combined cylinder affords a more compact design. DE 10 2005 044 708 A1 (corresponding to U.S. Pat. No. 7,523,999 B2) discloses a brake cylinder of this type, in which the function of the parking brake cylinder is integrated directly into the service brake cylinder. Here, the spring force accumulator spring is no longer actuated via a separate spring force accumulator piston, but rather likewise via the piston of the service brake cylinder. In order to release the parking brake, the SBS piston is loaded for a short time period by way of a special actuation with compressed air.
As described in the preceding text, the parking brake is released as a rule with the aid of compressed air. In addition, however, it also has to be possible to release the parking brake by a manual operation in the case of a pressure loss.
To this end, in the case of conventional combined cylinders, the spring is pulled back with the aid of a threaded spindle (what is known as the “release spindle”). As a result, the function of the service brake cylinder is not impaired.
This cannot be realized in such a simple way in the case of the compact combined cylinder, since the SBS piston and the spring force accumulator spring are connected to one another. If the spring were pulled back by a threaded spindle which is accessible from the outside, the SBS piston would also be blocked and, as a consequence, the SBS cylinder would no longer function.
A manually actuable release device is therefore advantageous to release the spring force accumulator spring manually, which manually actuable release device makes it possible to cancel the spring force accumulator action in the case of a pressure loss, without impairing the SBS function. Furthermore, it is possible to reestablish the PBS action by a manual operation after the release operation. The release device is also suitable, in particular, for compact combined cylinders which have a threaded spindle with a quick-action thread which is not self-locking. The quick-action thread primarily serves to make it possible to arrest the spring force accumulator spring in what is known as the release position. To this end, the threaded spindle is fixed by way of a pneumatically actuated locking mechanism. When the parking brake is engaged, the locking mechanism is ventilated, as a result of which the threaded spindle can be rotated and the spring force accumulator spring can be relieved. The threaded spindle is preferably also used for manually releasing the spring force accumulator spring. Here, the threaded spindle is set in rotation by an external introduction of force. Since it is a quick-action thread which is not self-locking here, the spindle would be rotated back again immediately, for example, when the wrench is turned and the spring force accumulator spring would therefore start acting again.
For the actuation of a brake cylinder of the generic type, separate elements are required in addition to the customary brake control system, which signifies a disadvantage.
The solution to this problem is the object of the invention.
According to the invention, a brake cylinder and method of operating same are provided for pneumatically actuated vehicle brakes, in particular for commercial vehicles, including a spring force accumulator brake section for carrying out parking brake operations by use of a spring force accumulator spring, and a service brake section for carrying out service brake operations which are actuated by compressed air. The spring force accumulator brake section and the service brake section are combined in a housing to form one structural unit. The housing is divided by a piston into two spaces, of which one of the two spaces serves as pressure space for actuating the service brake section. The spring force accumulator spring of the spring force accumulator section is arranged in the further space on the opposite side of the piston. The spring force accumulator spring acts in the space on a further spring force accumulator piston, which can be locked with respect to the piston by way of a pneumatically actuable locking mechanism and can be released from the locking mechanism by release of the latter, and which is connected directly or via further elements to a piston rod for actuating the vehicle brake. After the release of the locking mechanism, the spring force accumulator spring acts between the two pistons and displaces them relative to one another in the case of a parking brake operation. At least one or more pneumatic valves is integrated into the brake cylinder in order to actuate the brake cylinder.
The required independence can be realized by the integration of all or at least some of the components or elements for the special actuation of the compact combined cylinder.
The invention preferably integrates all the additionally necessary elements directly into the compact brake cylinder. It therefore provides improved cylinder control, which in principle does not require any special valve architecture on the remaining vehicle brake system outside the cylinder, with the result that the known construction of the valve architecture can be retained per se, since all the additional elements are integrated into the cylinder.
The brake cylinder is preferably supplemented merely by purely pneumatic/mechanical elements for actuation, and the use of electronic control components is avoided, in order to ensure functioning which is independent of the vehicle electrical system. It is possible in this way to design the controller such that all the different operating situations can be realized even without a current supply of the cylinder.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.